The invention relates to a tracer release method for monitoring the fluid flowrate in a downhole well conduit. Such a method is known from European patent application No. 0816631.
In the known tracer release method different types of tracers are embedded in claddings along the length of the well inflow zone. The claddings may be oil soluble substances which slowly dissolve in the well fluids and the amount of tracer released is then an indication of the amount oil and/or gas into the well at a particular place.
Drawbacks of the known method are that significant quantities of tracer and cladding are required to monitor the flow of well effluents, that significant workover operations are required to replace the cladded wall tubulars after depletion of tracer material and that the amount of tracer released is not an accurate reflection of the amount of fluid flowing through the well, but is also dependent on the temperature and composition of the well effluents.
It is observed that U.S. Pat. No. 4,846,279 discloses a method for injecting a treatment fluid into a lower end of a well by means of a bag which is compressed by a pressure difference between a downstream and an upstream location of the well and that U.S. Pat. No. 5,544,785 discloses a method for downhole injecting a hardening agent into a cement slurry using a container from which the agent is injected into the slurry by means of a venturi effect.
U.S. Pat. No. 4,166,216 discloses a method for injecting various oil and/or water mixible tracer materials into a production tubing by means of a injection tool that is temporarily suspended in the well from a wireline.
It is an object of the present invention to alleviate the drawbacks of the known tracer injection method and to provide a tracer release method that provides a more accurate reflection of the fluid flowrate, which can be more easily replaced, which is able to release an accurately dosed minimal amount of tracer material into the well effluents and which is able to transmit other well data than the fluid flowrate to a well fluid flow monitoring and survey system at the earth surface.